1. Field of the Invention
The invention relates to a self-emission type display device, for example, a display device using an organic electroluminescent element as a self-emissive element.
2. Description of the Related Art
An organic electroluminescent (referred to as “EL”, hereafter) display device using an organic EL element as a self-emissive element has been developed as a display device replacing a CRT or an LCD in recent years. Particularly, an active matrix type organic EL display device that has a driving transistor driving an organic EL element in response to a video signal has been developed.
Generally, there are a negative polarity video signal and a positive polarity video signal as the kinds of the video signal that is inputted to the organic EL display device, and the organic EL display devices conventionally need be provided for these negative and positive video signals respectively.
FIG. 5 is a circuit diagram of a pixel of the organic EL display device for the negative polarity video signal. The negative polarity video signal applied to a data line DL is applied to a gate of a P-channel type driving transistor 2A through an N-channel type pixel selection transistor 1 where on and off are controlled by a gate signal from a gate line GL. Then, a drive current corresponding to the negative polarity video signal flows in the driving transistor 2A, and then supplied to an organic EL element 3. The larger this drive current is, the higher the luminance when the organic EL element 3 emits light is.
In the negative polarity video signal, a reference potential Ref(H) on a high potential side corresponds to a black level, and a reference potential Ref(L) on a low potential side corresponds to a white level. Therefore, the driving transistor 2A is set to the P-channel type so that the drive current of the driving transistor becomes larger as the negative polarity video signal is lower.
On the other hand, FIG. 6 is a circuit diagram of a pixel of the organic EL display device for the positive polarity video signal. The positive polarity video signal applied to the data line DL is applied to a gate of an N-channel type driving transistor 2A through an N-channel type pixel selection transistor 1 where on and off are controlled by a gate signal from the gate line GL. Then, a drive current corresponding to the positive polarity video signal flows in the driving transistor 2A, and then supplied to the organic EL element 3. The larger this drive current is, the higher the luminance when the organic EL element 3 emits light is.
In the positive polarity video signal, a reference potential Ref(H) on a high potential side corresponds to a white level, and a reference potential Ref(L) on a low potential side corresponds to a black level. Therefore, the driving transistor 2A is set to the N-channel type so that the drive current of the driving transistor becomes larger as the positive polarity video signal is larger. The relevant technology is described in Japanese Patent Application Publication No. 2003-228328.
The organic EL display devices need be provided for the negative polarity video signal and the positive polarity video signal respectively as described above. That is, the organic EL display device of FIG. 5 for the negative polarity video signal can not be used for the positive polarity video signal, and the organic EL display device of FIG. 6 for the positive polarity video signal can not be used for the negative polarity video signal.